When the Jobsinator tucked his polo neck into his trousers and announced that the Apple iPad would arrive unlocked to any network and packing a GSM SIM-card slot, we thought we were in like Flynn -- on our next hop over the pond, we could pick up a 3G iPad and then pop in a SIM card from any of our fine, upstanding British networks.

Sadly, Apple has scuppered those plans by using a different kind of SIM in the iPad, called the micro SIM (pictured above). It's also known as the 3FF card, for 'third form factor' -- typical SIM cards (pictured top) were the second form factor, following the first credit card-sized cards. Micro SIMs are 12x15mm, while normal SIM cards pork out at 15x25mm.

The major benefit of the micro SIM is its size, says Yvon Avenel, editor of the SIM-card industry mag SmartCardsTrends. While we're sure the iPad has plenty of gear packed into its slim frame, we'd have to see inside to believe that a standard SIM card wasn't small enough -- after all, it fits into the iPhone.

We may just be feeling cynical after a long night of Apple coverage, but it seems that Apple is being intentionally contrary by selling an 'unlocked' iPad that uses a SIM card you can't buy anywhere -- effectively, this locks the iPad down more than the iPhone ever was.

On the other hand, networks who want to get in on the revenue that the data-hungry iPad would generate for them could start churning out micro SIM cards any time. O2 told us it didn't have any devices that use the cards now, but it planned to start providing micro SIM cards when the gadgets start showing up on our shores.

Update: The European Telecommunications Standards Institute (ETSI), which sets the
standards for SIM cards, tells us that except for the size of the plastic around the chip, micro SIM cards are identical to the SIM cards we normally find in phones.

That means in theory, nothing is stopping us from trimming down a standard SIM card and popping it in the iPad. We haven't tested this yet, so we can't guarantee it will work -- but as soon as we get our hands on the 3G iPad for a full review, we'll be giving it a try to confirm it.